Some findings from today's trip which was mainly motorway.
1. The direct drive gearing on the Crosstar is 2360 rpm (give or take a few rpm) at 62 mph (GPS speed - about 63.5 on the speedometer). The normal Jazz may be slightly different due to the different wheels / tyres.
2. By watching the road speed and the engine speed I've concluded that direct drive is used from around 42 mph (=1600 rpm) upwards provided that the power demand is within the engine's capability at the rpm corresponding to the road speed. This means gentle acceleration or modest hills although climbing the hill to junction 18 on the eastbound M4 in the low 60's was done at around 2800 rpm (ie not direct drive).
3. If the battery is at less than 60% charge then some power is used to top up the battery when running in direct drive. Only if the battery is at 60% or more charge does the animated power flow graphic clearly show it's in direct drive as there's no power flow to/from the battery.
4. Easing off slightly on the accelerator with the battery at 60% charge usually results in the vehicle going into EV mode until either the battery is down to 30% or there's significant pushing on the accelerator pedal.
5. The engine noise at 70 mph (about 2660 rpm in direct drive) is minimal although a firm push on the accelerator will get the engine into the noisy range (but still not as noisy as my HR-V which suggests better soundproofing).
6. I was unable to get any useful info on the engine warm-up time. The Torque app was unable to read the coolant temperature and I don't think the blue cold engine warning light came on at the journey start as it was a warm day.
7. As I expected based on the WLTP results, the mpg dropped noticeably once the speed was over about 60 mpg. I reckon about 65 mpg in the low 60's although that was into a 10 mph headwind.
8. The auto headlights didn't come on when I was stopped in traffic while under the motorway so Honda seem to have fixed that problem (I wait to see whether they come on at a sensible level of darkness).
The bad news is that trip confirmed what I felt on the previous 2 hour journey: The seats are worse than my HR-V. I commented on this to my front seat passenger who had reached the same conclusion. I'm going to be looking for a thin firm cushion to see if that fixes the comfort issue.
On a different subject, I put one of these LED bulbs
https://www.ebay.co.uk/itm/501-Led-Cob-White-T10-Xenon-Bulbs-W5w-Side-Light-Canbus-Error-Free-Wedge-194-168/382894921689 in the boot and it's a lot brighter than the original bulb. Given that the price is for 10, it makes Honda's £50 in the vehicle configurator accessories section (under Audio and Electronics) look a bit greedy. I've also put LED bulbs in the reversing lights but won't pass comment on their effectiveness until I need to reverse in darkness. I think the only remaining non-LED bulbs are the rear turn indicators. I'm not planning to change those due to (i) it's not obvious how to get to them and (ii) relatively expensive special bulbs are needed to avoid the flash rate going beserk.